Sandbox sims are sims provided for residents to build and test in, and are typically cleared of objects on a regular schedule to get rid of clutter. There are also smaller sandboxes that do not occupy an entire sim.
A large portion of Morris is designed as a sandbox for new residents to get a feel for the building tools, as it is a part of the main Welcome Area.
On November 18, 2003, Linden Lab announced that Cordova would replace Olive as the public sandbox. LL decided to retire Olive from sandbox duty and use it as a testing ground for the new prim limits that were later implemented in version 1.2.
On October 28, 2004, Ryan Linden announced the opening of the Newcomb and Goguen sandboxes. Goguen was added to relieve some load off of Cordova. Newcomb was created as a no-script sandbox to help make things a little more peaceful for people who just wanted to build without scripts.
A day later, on October 29, 2004, Ryan Linden announced the Island Sandbox, after a few residents (like Kex Godel) badgered LL on the forums to create a sandbox where people could conduct experiments without fear of affecting the mainland.
On October 19th, 2006, Cyn Linden announced the addition of Sandbox Island Extension, below Sandbox Island, and Sandbox Wanderton, below Sandbox Newcomb.